The present invention relates to a thermoplastic resin composition for extrusion molding such as sheet molding, film molding, pipe molding, profile extrusion, or blow molding. More particularly, the present invention is concerned with a thermoplastic resin composition for extrusion such as sheet molding, film molding, pipe molding, profile extrusion, or blow molding, superior in the balance of dynamically heat-treating an -olefin (co)polymer of C.sub.2 to C.sub.8 and, if desired, a rubbery substance in the presence of a specific closslinking agent and polyfunctional monomer. Examples of products obtained using the composition of the present invention include sheets for use in civil engineering and agricultural works, water-proof sheets, sheets for automobile interior materials typified by leather-like-sheets and instrument panel skin material; films formed by T-die method or inflation method; pipes such as corrugated pipes, lining pipes, straight pipe pipes, cheeses, hoses and elbows; profile extrusion such as mud guards; hollow containers such as duct hoses, bellows pipes, seasoning containers, shampoo containers and gasoline tanks; and automobile parts formed by various forming methods, including fender, door panel, protector, bumper fascia, energy absorber, air spoiler, side molding weather strip, shock absorber, dust boots, rack and pinion boots, rear finisher, sill, rear coater panel, engine hood, and trunk lid.
Thermoplastic resins, as materials superior in moldability, are utilized in a wide variety of industrial fields. Further the utilization field thereof has been expanded by blending thereof with various other resins and fillers for modification. And thermoplastic resin compositions are formed into various products, including sheets, films, pipes, profile-extrusion products and hollow products. Further, with diversified needs, there is now a demand for products having various characteristics namely, thermoplastic resin compositions having various characteristics. To meet this demand, attempts are being made more actively than before for modifying thermoplastic resins by blending them with various resins and fillers. At the same time, however, troubles caused by such blending are becoming more and more serious. For example, if a large amount of an inorganic filler is incorporated in a thermoplastic resin, the tensile elongation of the resulting composition will be deteriorated although it will be possible to improve the rigidity thereof. And if a thermoplastic resin is blended with a soft substance such as a rubbery substance, deterioration will result in point of heat resistance and mechanical strength although the improvement of impact resistance will be attainable. In order to minimize such deterioration of physical properties, there has been adopted a method of dynamically heat-treating a thermoplastic resin composition, allowing crosslinking to take place. By this method there is attained improvement of impact resistance, tensile strength and heat resistance, and rubbery properties are enhanced when rubber is incorporated in the composition. This is well known. Further, such blending, using not only inorganic fillers and rubbery substances but also other materials sometimes results in deteriorated surface appearance of shaped articles obtained because of incorporation therein of substances of different qualities. In such simple blends, their mechanical strength is somewhat improved but not effective, and there has been the problem of surface roughness.
An example of a method which utilizes a dynamic heat treatment is shown in Japanese Patent Publication No. 34210/1978 (U.S. Pat. No. 3,806,558). As shown therein, a free radical forming agent typified by an organic peroxide is generally used. Using organic peroxide non-crosslinking type resins such as polypropylene resins, as thermoplastic resins, is suitable for injection molding because the compositions obtained are superior particularly in fluidity. However, the organic peroxides remaining in the compositions deteriorate thermal stability and weathering resistance and undergo sudden thermal decomposition, resulting in that there occurs a molecular cutting reaction, thus leading to deterioration of mechanical properties such as yield tensile strength, bending strength and flexural modulus.
Moreover, in the case where such compositions are used in extrusion molding such as sheet molding, film molding, pipe molding, profile extrusion, or blow molding, there occurs deterioration of the anti drawdown characteristic, which leads to an unformable state in the extreme case. Besides, there arise such problems as surface roughness and deficient elongation of shaped articles. The conventional method in question is not applicable to organic peroxide crosslinking type resins such as polyethylene resins because an extreme crosslinking reaction proceeds and consequently the flow characteristics of the resulting compositions are deteriorated markedly. Or it is required to use an organic peroxide in an extremely small amount and thus the reaction control is very difficult. Also, an offensive odor of the shaped article obtained often causes a problem.
This conventional method further involves such problems as low stability and safety of a free radical forming agent during storage thereof and also during the dynamic heat treatment, as well as a thermal decomposition loss caused by the adhesion thereof to heated inner walls of a processing machine. It has been desired to solve this problem.
Thus, in the conventional simple blending method or crosslinking method for thermoplastic resins using crosslinking agents, the crosslinking agent exhibits drawbacks such as causing decomposition of the composition during the dynamic heat treatment, side reaction, offensive odor, or coloration, and hence the composition after the treatment cannot be said fully satisfactory in practical use. Therefore, improvements have been desired for obtaining superior thermoplastic resin compositions for extrusion molding such as sheet molding, film molding, pipe molding, profile extrusion, or blow molding.
It is the object of the present invention to provide a thermoplastic resin composition for extrusion molding such as sheet molding, film molding, pipe molding, profile extrusion, or blow molding, superior in the balance of mechanical properties and moldability.